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March 12, 1929. w. B. KIRKE ET AL SHEIATH CONNECTION IN ELECTRIC CABLE SYSTEMS Original Filed June 23, 1923' 1N VENTURE MLLA C55 Mfr/f5. fi/aso/vff: J54 fiv/ve'.

A TTOR/VE Y Reissued Mar. 12, 1929.

UNITED STATES PATENT OFFICE.

WALLACE B. KIBKE, 0F BRONXVILLE, AND HUDSON R. SEARING, OF NEW YORK, 11'. Y.

SHEATH CONNECTION LN ELECTRIC-CABLE SYSTEMS.

Original No. 1,592,371, dated July 13, 1926, Serial No. 647,246, filed June 23, 1923. Application for reissue filed November 4, 1927, Serial No. 231,148. v

Among the principal objects which the present invention has in view are: to reduce induced sheath currents and sheath losses; to avoid the accumulative effect of the induced voltages in said sheaths; to avoid the production of electric arcs in said sheaths; and to simplify and cheapen the construction of cable systems.

Fig. 1 is a schematic view showing a single phase cable system constructed and arranged in accordance with the present invention;

Fig. 2 is a similar view showing the inven tion as applied to a three-phase system;

Fig. 3 is a detailed view on enlarged scale showing a cover for the sheath gaps;

Fig. 4 is a longitudinal sectional view of the same;

Fig. 5 is a cross-section of the same, the sec tion being taken as on the line 5-5 in Fig. 3;

Figs. 6 and 7 are diagrams illustrating the. currents;

Figs. 8 and 9 are corresponding diagrams illustrating the sectional arrangement of the circuits.

When alternating current is delivered over single conductor cables enclosed in separate sheaths of electro-conductive material, the conductor current sets up E. M. in the sheath, said E. M. F. being proportional to the flux interleakage between sheaths, which gives rise to several efiects. If a continuous section of the sheath of one conductor is grounded at more than one point or if continuous sections of the sheaths of two or more phases are connected together or grounded.

from ground, a. potential will be established" between the sectionsor between a section and ground.

Thus in single conductor lead-covered cables installed in ductsconstructed of in-" sulating material. a. choice must be made between additional losses due to currents in the sheaths if bonded together or grounded at more than one point or protection from potentials generated between the sheaths and tions are connected, thus requiringadditional copper and oftentimes an additional duct.

The present invention describes a method of connecting sections of sheaths of singleconductor cables which allows a continuous metallic path along the sheath circuit but reduces the sheath losses to a negligible amount over what is normally met with when a con-- tinuous sheath is grounded at more than one point or connectedto another metallic conductor at more than one point.

Referring to the drawings and particularly to Fig. 1 thereof, it will be seen that the numeral 12 indicates one conductor and numeral 21 the return conductor of a given length of a single phase cable system suitably coated with an insulation 13 which in turn is surrounded by a metallic sheath 14. The sheath is preferably formed of lead as being a metal close in texture and readily bent.

To avoid the accumulation of voltage in duced in the sheath 14- by the passage of current through the conductors 12, over a considerable length of the sheath circuit, the sheath is divided into suitable lengths, the terminals 15 of the sectipns being spaced apart a suitable distance, thus exposing the insulation 13 at these points. To protect the insulation 13 and the conductor 12 therein from weather, insulating coatings 16 are introduced, filling the gap between the termini 15 of the sheath sections and spreading lineally over the ends of the sheath sectionsto be covered by the clamp caps 17 as seen best in Figs. 3 to 5 inclusive. Intermediate theends of the sheath sections 14 in single phase systems, the said sections of both conductors are united by a bond which consists preferably of asuitabie wire bridge 18, the ends of which are wound on the sheaths. These bonds may or may not be grounded.

lengths of the conductors. Fig. 6 illustrates the effect o f such connections. In all sections of the-sheath for the conductor 12 there is a pressure or voltage induced in the direction of the arrows 23 at the time that the induced voltage in all sections of the sheath for the conductors 21 will be in the opposite direction asshown by the arrows 24. By reason of the cross connections between the sections carrying voltages in opposite directions the induced voltage in the sheath circuit will be neutralized to a greater or less extent, thus reducing the sheath currents and consequent losses and reducing the potential .to ground at the ends of the sheath sections. The parts may be so proportioned and connected together and to ground as to practically prevent any flowing of sheath currents. The conductors 12 and 21 are the outgoing and return conductors of 'a circuit in which at a given instant the current flows in the direc- Y tions of the arrows 25 and 26.

While the bonds 18 are shown in the drawing as being grounded at adjacent points where the sheath potential has been reduced to zero, as shown by numerals 22, this is not always necessary and only such points are grounded as are required in practice. Systems of two orany even number of phases can be I considered as two or more single phase systems by connecting together sheath sections of conductors of opposite polarity.

When using a system having three or an odd number of phases the jumpers 19 are serially installed, that is to say,'the sheath section on phase number 1, disposed in ad vance or at the opposite side of the sheath gaps. T hesheath section of phase number 2 is in a similar manner connected with the sheath section ofphase number 3in advance of the sheath gap, while the sheath section of phase number 3, is now connected by a jumper 20 with the section of phase number 1 at the advanced side of the. gaps. In this manner the sheath sections of a three phase system are connected and in a similar manner for a system having a greater odd number of bases.

Fig. 7 illustrates this arrangement, the conductors for the three phases being indicated at 1, 2 and 3 and their sheath sections at 14. The currents in the conductors are represented by the arrows 27,28 and 29. The value of thethree-phase currents is taken for representationat the instant when the outgoing current 27 is twice the magnitude of the return currents 28 and 29 as indicated by the comparative lengths of the arrows. At any other instant the three-phase currents will also be balanced, as is well understood. The three-phase currents 27, 28 and 29 induce voltages in the respective sheath sections which are represented at a given instant by the arrows 30, 31 and 32 respectively. The sheath T5 circuit is therefore composed of three sections, one in each phase, or it may be of several lengths, each length having three such sections; and for each such circuit there will be an induced voltage in one section which is. equal and opposite in direction to the induced voltage in the other two sections. It is thus possible to proportion the parts so as to fully counterbalance the voltages in the sheath sections. The induced voltages in any three connected sheath sections neutralize each other in the same manner as the mesh voltages of the delta-connected bank of transformers. The points at which the cross-connections 18 are located are nodal points between one section and the next where practically no volta 'e exists, neither to ground nor between the p ases of adjacent cable sheaths. At these points the three lines may be separately grounded, which would have the same effect as bonding them to one another; or they may be bonded by the connection 18, without grounding; but preferably they are crossconnected and also grounded as shown.

Figs. 8 and 9 are similar to Figs. 6 and 7 respectively, but showing a greaterlength of line and a number of sections. The'circuit should (preferably, though not necessarily) be arranged so as to comprise a whole number (not a fractional number) of complete sections. Taking Fig. 9, for example, where each section between successive nodal points and connectors 18 is divided into three subsections which are serially connected in transposed relation as described, the circuit should comprise a whole number of such sections or a multiple of three such sub-sections as are indicated at 33, 34 and 35 respectively. This is the more important where the cross-connections 18 are not 'utilized. Otherwise the 115 voltages-in the sub-sections of the complete line would not balance one another. p The end sub-sections 35 and 33 of the ad joining sections are continuously connected balanced according to the inequality of the lengths. But the induced sheath voltages will still be partially balanced and the resultant sheath currents (it being understood that the current flowing is the function or restood that while we have shown and described the jumpers 19 as constructed of independent wire elements a similar result can be obtained by employing strips of the sheath 14 formedintegral with one of the said sheaths or integral'with the sheath gap covers.

By referring to Figs. 1 and 2, it will be seen that in case a fault should occur between a conductor and sheath each sheath section has two paths for the return of the short. circuit current to ground. Heretofore if a sheath'section had more than one connection to ground, sheath currents and losses would occur. In case one of the groundconnections or jumpers from one sheath section to other sheath sections became opencircuited, there still remains a second circuit'to ground which will carry away fault currents and prevent the sheath from building up to dangerous potentials.

The fact also that each sheath gap is bridged by metallic connections, all of which unite at one or more common ground points, reduces the potential difference between the ends of adjacent sheath sections and allows the sheath gap to be designed to withstand only small potential differences when a. fault occurs in any section from conductor to sheath.

.sheaths.

The inventionis particularly designed for single-conductor cables with independent sheaths, such as are commonly used for the transmission of power in the form of alternating current of extremely high voltages.

\Vhcn the lead sheaths of such cables are grounded and bonded together in the usual way there is, a transformer action between the conductors" of the line and their bonded The efl'ectjs to give rise to electrical losses in the sheath which may amount to as much as forty per cent of the electrical losses in the .con uctors themselves. These factory met odhas been previously found of avoiding such losses without\ sacrificing protection of the system and requiring additional expense for auxiliary ground wire.

Various modifications may be made by those skilled in the art without departing from the invention as defined in the following claims.

\Vhat we claim is:

1. An electric circuit for transmitting three-phase currents comprising three insulated conductors enclosed in metallic sheaths physically separated from each other, the circuit comprising a whole number of complete sections in each of which the sheaths are in three sub-sections of approximately equal length, thesheath at each conductor in a sub-section being insulated from the sheath of the same conductor in the adjoining subsection and the sheaths in each section being serially connected to one another in trans posed relation so that the induced voltages in the serially connected sheaths in the section tend to oppose eachother and to prevent the flow of current through the sheaths.

2. An electric circuit for transmitting three-phase currents comprising three insulated conductors enclosed in metallic sheaths physically separated from each other, the circuit comprising a number of sections in each of which the sheaths are in three subsections of approximately equal length, the sheath ofeach conductor in a sub-section being insulated from the sheath of the same conductor in the adjoining sub-section and the sheaths in .eaclnsection being serially connccted to one another in transposed relation so that the induced voltages in the serially connected sheaths in the section tend to oppose each other and to prevent the flow of current, the end sub-sections of adjoining sections of the sheath being continuous so as to make an unbroken line of aproximately double length.

3. An electric circuit for tranmitting three'phase currents comprisingthree in sulatcd conductors enclosed in metallic sheaths physically separated from each other, the circuit comprising a number of sections of alternate single and double lengths, the sheath of each section being insulated from the sheath of the same conductor in the adjoining section and the sheath sections of each phase being serially connected with the adjoining sheath sections of the other phases in transposed relation so that the induced voltages in the serially connected sections of sheath tend to oppose each other and to prevent the flow of current.

4. An electric circuit for transmitting three-phase currents comprising three insulated conductors enclosed in metallic sheaths physicallyscparated from each other, the circuit comprising a number of sections in each of which the sheaths are in three subsections of approximately equal length, the sheath of eachconductor in a sub-section being insulated from the sheath of the same conductor in the adjoining sub-section and the sub-sections of the sheaths in each section be sheath being electrically connected so as to ing serially connected to one another in transmake an-unbroken sheath circuit of approxiposed relation so that the induced voltages mately double length.

in the serially connected sub-sections of the In witness whereof, we have hereunto sheaths in the section tend to oppose each signed our names. other and to prevent the flow of current, the r WALLACE B. KIRKE.

end sub-sections of adjoining sections of the HUDSON R. SEARING. 

